Liquid ring pumps are well known. U.S. Pat. No. 4,498,844, Bissell discloses a liquid ring pump with a conical port member. The conical port member has a vent re-circulation port in addition to the conventional intake and discharge ports. U.S. Pat. No. 4,498,844 is incorporated herein in its entirety.
The pump shown in FIG. 1 is of a known configuration of a conical liquid ring pump. FIG. 1 is a vertically oriented sectional view, taken along a plane parallel to the pump's shaft. FIG. 1a shows that the cross-section is taken along line 100. Cross section line 100 thus provides the perspective point for FIG. 1.
The pump has a first head 20 and a second head 22. Each head has a gas inlet 20a, 22a. Each head has a gas discharge 20b, 22b. The heads 20, 22 are located at the axial ends of the liquid ring pump. Located axially between the pump heads 20, 22 is a body or housing 23. Located within the housing is a rotor 25. The rotor 25 has rotor blades 25a. The rotor blades 25a extend from a hub 25b. 
The body or housing 23 provides a chamber (working chamber) in which the rotor 25 rotates to draw air or gas 26 through gas inlets 20a, 22a into the working chamber. The gas 26 is then exhausted from the working chamber through gas discharge outlets 20b, 22b. 
As can be seen, the gas 26 is drawn into the working chamber through conical port members 27, 28. The gas is also exhausted from the working chamber through conical port members 27, 28. The chamber is divided into a first working chamber 23a and a second working chamber 23b by rotor shroud 25c and lobe shroud 23c. 
Sealing liquid 29, see FIG. 2, is in the working chamber. As the rotor 25 rotates, the sealing liquid 29 is formed into a liquid ring within the working chamber. The liquid ring takes an eccentric shape that diverges and converges in the radial direction relative to shaft 30 of the liquid ring pump. Where the sealing liquid 29 is diverging from the shaft 30, the resulting reduced pressure in the spaces between adjacent rotor blades of the rotor assembly (buckets) constitutes a gas intake zone. Where the sealing liquid 29 is converging towards the shaft 30, the resulting increased pressure in the spaces between the adjacent rotor blades (buckets) constitutes a gas compression zone. U.S. Pat. No. 4,850,808, Schultz, provides an example of a conical liquid ring pump. U.S. Pat. No. 4,850,808 is incorporated herein in its entirety.
The liquid ring pump shown in FIG. 1 has sealing liquid entry or introduction paths 31 which allow sealant 29 to enter the working chamber. The entering sealant 29 passes through the heads and conical port member. Although the sealing liquid 29 is shown entering only through head 20 and conical member 27, it could enter through head 22 and conical member 28.
In addition to having sealing liquid introduction pathways 31, the pump of FIG. 1 also has liquid vent paths to allow liquid to exit the working chamber during operation of the pump. Prior art FIG. 2 shows a schematic of sealing liquid 29 exiting the working chamber through sealing liquid vent path 33. The existing heads 20, 22 are symmetrical about the vertical axis permitting one head design to be used on either axial end of the pump. Depending on the direction of rotation, passages in the head are currently used for either introducing or venting the sealing liquid 29.
The design compression ratio is a ratio of the design discharge pressure to the design suction pressure. The operating compression ratio is a ratio of the operating discharge pressure to the operating suction pressure. In practice the pressure at discharge remains constant and is usually the atmospheric pressure. The suction pressure will vary depending on application.
It is known that a pump having a fixed discharge port and an operating compression ratio less than the design compression ratio will have increased pressure within the working chamber. Increased pressure requires the use of additional pump power. To minimize the need for increased pump power, the prior art, as shown in FIGS. 1 and 2 has compressant (sealing liquid) vent paths or built in liquid leakage paths to allow for the sealing liquid to exit the working chamber and reduce the pressure within the working chamber and within the buckets. Accordingly, the venting of the sealing liquid accommodates varying compression ratios experienced by the pump during operation.
The use of compressant or sealing liquid vent paths (liquid leakage paths) has several draw backs. Venting requires a balancing act of continually releasing and replenishing the seal liquid in order to achieve an appropriate pressure within the working chamber. If the seal liquid flow rate is increased over the normal flow rate, then the power control function of the liquid venting method is overcome and pump power can increase at low compression ratios where it can overload the drive system. Further a sudden drop in vacuum pressure from the design compression ratio to a low compression ratio results in a period in which the pump has more liquid in it than the steady state low compression ratio condition. The excess liquid can result in overloads to the drive equipment. Also, if the seal liquid to the pump is reduced, the flow out through the liquid vent paths results in diminished sealing within the pump and the gas volume pumped is reduced.